Viral load, also known as viral burden, viral titre or viral titer, is a numerical expression of the quantity of virus in a given volume. It is often expressed as viral particles, or infectious particles per mL depending on the type of assay.
A higher viral burden, titre, or viral load often correlates with the severity of an active viral infection. The quantity of virus / mL can be calculated by estimating the live amount of virus in an involved body fluid. For example, it can be given in RNA copies per millilitre of blood plasma. Tracking viral load is used to monitor therapy during chronic viral infections, and in immunocompromised patients such as those recovering from bone marrow or solid organ transplantation. Currently, routine testing is available for HIV-1, cytomegalovirus, hepatitis B virus, and hepatitis C virus.
Viral load monitoring for HIV is of particular interest in the treatment of people with HIV, as this is continually discussed in the context of management of HIV/AIDS.